1. Field of the Invention
The invention relates to a process for preparing in aqueous emulsion a bitumen/polymer binder with continuous three-dimensional polymeric structure. It also relates to the application of this binder to the production of facings and in particular of road surfacings, of hot- or cold-poured bituminous mixes or else of waterproof facings.
2. Background of the Invention
The use of bituminous binders either in maintenance facings as a surface coat or as a very thin bituminous mix, or as a thicker structural layer of bituminous mix, is only possible if these binders possess the requisite properties of elasticity and plasticity.
The road binders consisting of conventional bitumens do not retain sufficient elasticity and exhibit a plasticity range which is too narrow. It is known that the characteristics of such road binders can be greatly improved by incorporating into them a polymer of elastomeric type which may be one such as butyl, polybutadiene, polyisoprene or polyisobutene rubber, ethylene/vinyl acetate copolymer, polyacrylate, polymethacrylate, polychloroprene, polynorbornene, ethylene/propylene/diene (EPDM) terpolymer and advantageously a random or block copolymer of styrene and of a conjugated diene, the modified binders thus obtained being commonly referred to as bitumen/polymer binders.
The following quantities are generally used for characterizing the properties of bituminous binders:
penetration, expressed in tenths of a millimeter and determined according to NF standard T 66004, PA1 ring and ball softening point, expressed in .degree. C. and determined according to NF standard T 66008, PA1 Fraass brittle point, expressed in .degree. C. and determined according to IP standard 80/53. PA1 threshold stress (.sigma.t), expressed in bars PA1 threshold elongation (.epsilon.t), expressed in % PA1 breaking stress (.sigma.b), expressed in bars PA1 elongation at break (.epsilon.b), expressed in %
The temperature difference between the Fraass point and the ring and ball softening point defines the plasticity range of the bituminous binder.
Binders of the bitumen/polymer type can additionally be characterized by rheological tensile tests according to NF standard T 46002 allowing the following quantities to be determined:
It is known that an increase in the elastic properties of bituminous binders results in an improvement in the plucking strength of the granulates of the surface coatings and an improvement in the fatigue cracking resistance or the thermal shrinkage cracking resistance of the mixes. In addition, a ring and ball softening point value of the binder which is higher than the maximum temperatures (approximately 60.degree. C. to 70.degree. C.) encountered on the carriageway makes it possible to combat effectively the continuous creep resulting in the rutting of the mixes, and the rising of the binders onto the surface coatings, resulting in the phenomenon of bleeding. The first two points referred to are very important where economics are concerned, because they are at the source of the deterioration of the structure and of the load-carrying quality of the carriageway. The two latter points are themselves related to the important problem of safety, related to the surface roughness and to the surface uniformity of the surfacing.
The bituminous binders, even of the bitumen/polymer type, which are employed at the present time in road applications do not have the optimum characteristics which would make it possible to meet the above-mentioned requirements.
It is known to produce bituminous binders exhibiting such optimum characteristics for waterproofing applications, by incorporating a polymer in a quantity of more than 10% by weight into a mixture of directly distilled bitumen and oxidized bitumen. Such bituminous binders employed in the waterproofing industry cannot be employed in road building and road maintenance techniques essentially because their viscosity is too high. It is not possible, in fact, to spread a uniform layer of such a binder to produce a surface coating by relying on currently known spreading techniques for hot applications. Moreover, the formulation of the binder film permitting the coating of granulates in a hot-mixing plant is also not possible, because of the very high viscosity of the binder. Finally, the means for lowering this high viscosity of the binder by emulsification also cannot be envisaged with the technology which permits production rates compatible with the reality of road building and road maintenance.
According to the invention a process has been found which makes it possible to prepare in aqueous emulsion a bituminous binder of the bitumen/polymer type which, on the one hand, has a continuous three-dimensional polymeric structure endowing the binder with high viscosity, elasticity and ring and ball softening point values bringing this binder closer to the bituminous binders produced for use in waterproofing and which, on the other hand, does not exhibit the disadvantages of application of these binders which are employed in waterproofing.
In particular, the improved elastic properties of the bitumen/polymer binder produced according to the invention endow the bituminous mixes manufactured by employing this binder with a markedly improved fatigue strength. In addition, the high value of the ring and ball softening point of the binder permits a considerable reduction in the rutting of carriageways produced from this binder. Finally, the said binder has a very high cohesion which makes it possible to produce surfacings of satisfactory characteristics even with very large particle sizes, for example 10/14 mm, of the granulates used in combination with the binder.